Leetcode Day 23 - Greedy: Basic Applications
Fundamental greedy problems: 455 Assign Cookies | 376 Wiggle Subsequence | 53 Maximum Subarray
Greedy Algorithm
| Diff | Problem | Python | Java |
|---|---|---|---|
 | 455 Assign Cookies | ✅ | |
 | 376 Wiggle Subsequence | ✅ | |
| 53 Maximum Subarray | ✅ |
Assign Cookies
Assume you are an awesome parent and want to give your children some cookies. But, you should give each child at most one cookie.
Each child i has a greed factor g[i], which is the minimum size of a cookie that the child will be content with; and each cookie j has a size s[j]. If s[j] >= g[i], we can assign the cookie j to the child i, and the child i will be content. Your goal is to maximize the number of your content children and output the maximum number.
Example 1
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Input: g = [1,2,3], s = [1,1]
Output: 1
Explanation: You have 3 children and 2 cookies. The greed factors of 3 children are 1, 2, 3.
And even though you have 2 cookies, since their size is both 1, you could only make the child whose greed factor is 1 content.
You need to output 1.
Example 2
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Input: g = [1,2], s = [1,2,3]
Output: 2
Explanation: You have 2 children and 3 cookies. The greed factors of 2 children are 1, 2.
You have 3 cookies and their sizes are big enough to gratify all of the children,
You need to output 2.
Solution
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class Solution(object):
def findContentChildren(self, g, s):
g.sort()
s.sort()
i = 0
count = 0
ls = len(s)
for child in g:
while i < ls:
i += 1
if s[i - 1] >= child:
count += 1
break
return count
Wiggle Subsequence
A wiggle sequence is a sequence where the differences between successive numbers strictly alternate between positive and negative. The first difference (if one exists) may be either positive or negative. A sequence with one element and a sequence with two non-equal elements are trivially wiggle sequences.
- For example,
[1, 7, 4, 9, 2, 5]is a wiggle sequence because the differences(6, -3, 5, -7, 3)alternate between positive and negative. - In contrast,
[1, 4, 7, 2, 5]and[1, 7, 4, 5, 5]are not wiggle sequences. The first is not because its first two differences are positive, and the second is not because its last difference is zero.
A subsequence is obtained by deleting some elements (possibly zero) from the original sequence, leaving the remaining elements in their original order.
Given an integer array nums, return the length of the longest wiggle subsequence of nums.
Example 1
Input: nums = [1,7,4,9,2,5]
Output: 6
Explanation: The entire sequence is a wiggle sequence with differences (6, -3, 5, -7, 3).
Example 2
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Input: nums = [1,17,5,10,13,15,10,5,16,8]
Output: 7
Explanation: There are several subsequences that achieve this length.
One is [1, 17, 10, 13, 10, 16, 8] with differences (16, -7, 3, -3, 6, -8).
Example 3
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Input: nums = [1,2,3,4,5,6,7,8,9]
Output: 2
Solution
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class Solution(object):
def wiggleMaxLength(self, nums):
if len(nums) == 1:
return 1
if len(nums) == 2:
return 2 if nums[1] - nums[0] != 0 else 1
prv_diff = nums[1] - nums[0]
count = 2 if prv_diff != 0 else 1
for i in range(2,len(nums)):
cur_diff = nums[i] - nums[i - 1]
if cur_diff * prv_diff < 0 or (count == 1 and cur_diff != 0):
count += 1
prv_diff = cur_diff
if count == 1:
prv_diff = cur_diff
return count
Similar Questions
| Diff | Similar Questions | Python | Java |
|---|---|---|---|
| 2149 Rearrange Array Elements by Sign5 |
Maximum Subarray
Given an integer array nums, find the subarray with the largest sum, and return its sum.
Example 1
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Input: nums = [-2,1,-3,4,-1,2,1,-5,4]
Output: 6
Explanation: The subarray [4,-1,2,1] has the largest sum 6.
Example 2
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Input: nums = [1]
Output: 1
Explanation: The subarray [1] has the largest sum 1.
Example 3
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Input: nums = [5,4,-1,7,8]
Output: 23
Explanation: The subarray [5,4,-1,7,8] has the largest sum 23.
Solution
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class Solution(object):
def maxSubArray(self, nums):
if len(nums) == 1:
return nums[0]
cur_sum = min(nums[0],0)
max_sum = cur_sum
flag = False
for fast in range(len(nums)):
if cur_sum <= 0 and not flag and max_sum <= 0:
max_sum = max(nums[fast], max_sum)
cur_sum = max_sum
continue
if nums[fast] < 0:
if not flag:
max_sum = max(max_sum, cur_sum)
flag = True
cur_sum += nums[fast]
continue
if flag:
flag = False
if cur_sum <= 0:
cur_sum = 0
cur_sum += nums[fast]
max_sum = max(max_sum, cur_sum)
return max_sum
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class Solution:
def maxSubArray(self, nums):
result = float('-inf')
count = 0
for i in range(len(nums)):
count += nums[i]
if count > result:
result = count
if count <= 0:
count = 0
return result
Similar Questions
| Diff | Similar Questions | Python | Java |
|---|---|---|---|
| 152 Maximum Product Subarray8 | ||
| 978 Longest Turbulent Subarray9 | ||
 | 2321 Maximum Score Of Spliced Array10 |
Reference
Leetcode-455 Assign Cookies: https://leetcode.com/problems/assign-cookies/description/. ↩︎
代码随想录-分发饼干: https://programmercarl.com/0455.分发饼干.html. ↩︎
Leetcode-376 Wiggle Subsequence: https://leetcode.com/problems/wiggle-subsequence/description/. ↩︎
代码随想录-摆动序列: https://programmercarl.com/0376.摆动序列.html. ↩︎
Leetcode-2149 Rearrange Array Elements by Sign: https://leetcode.com/problems/rearrange-array-elements-by-sign/. ↩︎
Leetcode-53 Maximum Subarray: https://leetcode.com/problems/maximum-subarray/description/. ↩︎
代码随想录-最大子序和: https://programmercarl.com/0053.最大子序和.html. ↩︎
Leetcode-152 Maximum Product Subarray: https://leetcode.com/problems/maximum-product-subarray/description/. ↩︎
Leetcode-978 Longest Turbulent Subarray: https://leetcode.com/problems/longest-turbulent-subarray/description/. ↩︎
Leetcode-2321 Maximum Score Of Spliced Array: https://leetcode.com/problems/maximum-score-of-spliced-array/. ↩︎